Research Accomplishments

Amebiasis, caused by the eukaryotic parasite Entamoeba histolytica, is an enormous global medical problem because poor sanitary conditions and unsafe hygiene practices exist in many parts of the world. According to the World Health Organization, 50 million people in India, Southeast Asia, Africa, and Latin America suffer from amebic dysentery and amebiasis causes the death of at least 100,000 individuals each year. E. histolytica trophozoites normally inhabit the colon and spend their time in the host as a non-pathogenic commensal. However, the reasons why these trophozoites become virulent and invasive are unknown. E. histolytica is challenged in the host environment due to fluctuations in partial pressure of oxygen, changes in glucose concentration and changes in the composition of the microbiota. The activation of innate immune responses against the parasite leads to the production of reactive oxygen species, nitric oxide by macrophages, complement activation and phagocytosis, and heat shock responses. The parasite must be capable of adapting to the demand of surrounding environment in order to survive. This adaptive response of the parasite provides a shield against the host response as well as aids in their survival. Since 2000, my group is interested in studying the mechanisms of adaptation of the parasite to environmental stresses with an emphasis on the role epigenetic regulation and more specifically, tRNA modifications, in this process.
We have demonstrated that the parasite DNA/tRNAasp methyltransferase (Ehmeth) is a central player in the resistance of the parasite to oxidative and nitrosative stresses by turning on stress response (as exemplified by the expression of the heat shock protein 70). Our laboratory has been the first to understand how this protein is regulated by the glycolytic enzyme enolase. This discovery led to the publication of a series of articles about the ability of the parasite to adapt to glucose starvation and the role of glucose in the regulation of the parasite’s virulence. The fact that Ehmeth contributes to the resistance of the parasite to oxidative and nitrosative stresses incite us to get insights into the S-nitroso-proteome and into the redox-proteome of the parasite by using the SNO and OX RAC approaches. Consequently, we discovered that proteins involved in the virulence of the parasite like the Gal/GalNAc-specific lectin, arginase and actin were redox-regulated. Following colonization of the gut, the parasite is constantly interacting with the gut microbiota whose contribution to the manifestation of disease is poorly understood. The trophozoites are quite selective in their interactions with different bacterial species and only those bacteria which have the appropriate recognition molecules get attached to the trophozoites and are ingested. Whereas our work provided insights into the mechanisms used by the parasite to cope with oxidative and nitrosative stresses during infection, knowledge about the contribution of bacteria to these mechanisms is scanty. We have recently demonstrated that E. coli malate dehydrogenase and its product, oxaloacetate, are key elements of the E. coli-mediated resistance of E. histolytica to oxidative stress and virulence. Work is in progress to study additional prokaryotic metabolites that confer oxidative stress resistance to the parasite.